Python Tricks

Using casting functions to determine the datatype of a token

When you implement a parser, it is very likely that you need to figure out what type your token is.

When you try to determine if the token is an integer, instead of using isdigit(), consider using a try / except block with casting functions like:

def is_integer(token):
    try:
        int(token)
        return True
    except ValueError:
        return False

Why? When the token is a negative number, isdigit() does not consider it an integer and returns False.

>>> '-1'.isdigit()
False
>>> int('-1')
-1